Terminate process on invalid netlink response from kernel [BZ #12926]

The recvmsg system calls for netlink sockets have been particularly
prone to picking up unrelated data after a file descriptor race
(where the descriptor is closed and reopened concurrently in a
multi-threaded process, as the result of a file descriptor
management issue elsewhere).  This commit adds additional error
checking and aborts the process if a datagram of unexpected length
(without the netlink header) is received, or an error code which
cannot happen due to the way the netlink socket is used.

	[BZ #12926]
	Terminate process on invalid netlink response.
	* sysdeps/unix/sysv/linux/netlinkaccess.h
	(__netlink_assert_response): Declare.
	* sysdeps/unix/sysv/linux/netlink_assert_response.c: New file.
	* sysdeps/unix/sysv/linux/Makefile [$(subdir) == inet]
	(sysdep_routines): Add netlink_assert_response.
	* sysdeps/unix/sysv/linux/check_native.c (__check_native): Call
	__netlink_assert_response.
	* sysdeps/unix/sysv/linux/check_pf.c (make_request): Likewise.
	* sysdeps/unix/sysv/linux/ifaddrs.c (__netlink_request): Likewise.
	* sysdeps/unix/sysv/linux/Versions (GLIBC_PRIVATE): Add
	__netlink_assert_response.

ChangeLog

@@ -1,3 +1,19 @@
+2015-11-09  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #12926]
+	Terminate process on invalid netlink response.
+	* sysdeps/unix/sysv/linux/netlinkaccess.h
+	(__netlink_assert_response): Declare.
+	* sysdeps/unix/sysv/linux/netlink_assert_response.c: New file.
+	* sysdeps/unix/sysv/linux/Makefile [$(subdir) == inet]
+	(sysdep_routines): Add netlink_assert_response.
+	* sysdeps/unix/sysv/linux/check_native.c (__check_native): Call
+	__netlink_assert_response.
+	* sysdeps/unix/sysv/linux/check_pf.c (make_request): Likewise.
+	* sysdeps/unix/sysv/linux/ifaddrs.c (__netlink_request): Likewise.
+	* sysdeps/unix/sysv/linux/Versions (GLIBC_PRIVATE): Add
+	__netlink_assert_response.
+
 2015-11-07  H.J. Lu  <hongjiu.lu@intel.com>
 
 	[BZ #19178]

NEWS

@@ -11,6 +11,14 @@ Version 2.23
   the following new symbols are used: fts64_children, fts64_close,
   fts64_open, fts64_read and fts64_set.
 
+* getaddrinfo now detects certain invalid responses on an internal netlink
+  socket.  If such responses are received, an affected process will
+  terminate with an error message of "Unexpected error <number> on netlink
+  descriptor <number>" or "Unexpected netlink response of size <number> on
+  descriptor <number>".  The most likely cause for these errors is a
+  multi-threaded application which erroneously closes and reuses the netlink
+  file descriptor while it is used by getaddrinfo.
+
 * A defect in the malloc implementation, present since glibc 2.15 (2012) or
   glibc 2.10 via --enable-experimental-malloc (2009), could result in the
   unnecessary serialization of memory allocation requests across threads.

sysdeps/unix/sysv/linux/Makefile

@@ -151,6 +151,7 @@ sysdep_headers += netinet/if_fddi.h netinet/if_tr.h \
 		  netipx/ipx.h netash/ash.h netax25/ax25.h netatalk/at.h \
 		  netrom/netrom.h netpacket/packet.h netrose/rose.h \
 		  neteconet/ec.h netiucv/iucv.h
+sysdep_routines += netlink_assert_response
 endif
 
 # Don't compile the ctype glue code, since there is no old non-GNU C library.

sysdeps/unix/sysv/linux/Versions

@@ -169,5 +169,7 @@ libc {
   GLIBC_PRIVATE {
     # functions used in other libraries
     __syscall_rt_sigqueueinfo;
+    # functions used by nscd
+    __netlink_assert_response;
   }
 }

sysdeps/unix/sysv/linux/check_native.c

@@ -35,6 +35,7 @@
 
 #include <not-cancel.h>
 
+#include "netlinkaccess.h"
 
 void
 __check_native (uint32_t a1_index, int *a1_native,
@@ -117,6 +118,7 @@ __check_native (uint32_t a1_index, int *a1_native,
 	};
 
       ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
+      __netlink_assert_response (fd, read_len);
       if (read_len < 0)
 	goto out_fail;
 

sysdeps/unix/sysv/linux/check_pf.c

@@ -36,6 +36,7 @@
 #include <atomic.h>
 #include <nscd/nscd-client.h>
 
+#include "netlinkaccess.h"
 
 #ifndef IFA_F_HOMEADDRESS
 # define IFA_F_HOMEADDRESS 0
@@ -164,7 +165,8 @@ make_request (int fd, pid_t pid)
 	};
 
       ssize_t read_len = TEMP_FAILURE_RETRY (__recvmsg (fd, &msg, 0));
-      if (read_len <= 0)
+      __netlink_assert_response (fd, read_len);
+      if (read_len < 0)
 	goto out_fail;
 
       if (msg.msg_flags & MSG_TRUNC)

sysdeps/unix/sysv/linux/ifaddrs.c

@@ -168,6 +168,7 @@ __netlink_request (struct netlink_handle *h, int type)
 	};
 
       read_len = TEMP_FAILURE_RETRY (__recvmsg (h->fd, &msg, 0));
+      __netlink_assert_response (h->fd, read_len);
       if (read_len < 0)
 	goto out_fail;
 

sysdeps/unix/sysv/linux/netlink_assert_response.c

@@ -0,0 +1,106 @@
+/* Check recvmsg results for netlink sockets.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/socket.h>
+
+#include "netlinkaccess.h"
+
+static int
+get_address_family (int fd)
+{
+  struct sockaddr_storage sa;
+  socklen_t sa_len = sizeof (sa);
+  if (__getsockname (fd, (struct sockaddr *) &sa, &sa_len) < 0)
+    return -1;
+  /* Check that the socket family number is preserved despite in-band
+     signaling.  */
+  _Static_assert (sizeof (sa.ss_family) < sizeof (int), "address family size");
+  _Static_assert (0 < (__typeof__ (sa.ss_family)) -1,
+                  "address family unsigned");
+  return sa.ss_family;
+}
+
+void
+internal_function
+__netlink_assert_response (int fd, ssize_t result)
+{
+  if (result < 0)
+    {
+      /* Check if the error is unexpected.  */
+      bool terminate = false;
+      int error_code = errno;
+      int family = get_address_family (fd);
+      if (family != AF_NETLINK)
+        /* If the address family does not match (or getsockname
+           failed), report the original error.  */
+        terminate = true;
+      else if (error_code == EBADF
+          || error_code == ENOTCONN
+          || error_code == ENOTSOCK
+          || error_code == ECONNREFUSED)
+        /* These errors indicate that the descriptor is not a
+           connected socket.  */
+        terminate = true;
+      else if (error_code == EAGAIN || error_code == EWOULDBLOCK)
+        {
+          /* The kernel might return EAGAIN for other reasons than a
+             non-blocking socket.  But if the socket is not blocking,
+             it is not ours, so report the error.  */
+          int mode = __fcntl (fd, F_GETFL, 0);
+          if (mode < 0 || (mode & O_NONBLOCK) != 0)
+            terminate = true;
+        }
+      if (terminate)
+        {
+          char message[200];
+          if (family < 0)
+            __snprintf (message, sizeof (message),
+                        "Unexpected error %d on netlink descriptor %d",
+                        error_code, fd);
+          else
+            __snprintf (message, sizeof (message),
+                        "Unexpected error %d on netlink descriptor %d"
+                        " (address family %d)",
+                        error_code, fd, family);
+          __libc_fatal (message);
+        }
+      else
+        /* Restore orignal errno value.  */
+        __set_errno (error_code);
+    }
+  else if (result < sizeof (struct nlmsghdr))
+    {
+      char message[200];
+      int family = get_address_family (fd);
+      if (family < 0)
+          __snprintf (message, sizeof (message),
+                      "Unexpected netlink response of size %zd"
+                      " on descriptor %d",
+                      result, fd);
+      else
+          __snprintf (message, sizeof (message),
+                      "Unexpected netlink response of size %zd"
+                      " on descriptor %d (address family %d)",
+                      result, fd, family);
+      __libc_fatal (message);
+    }
+}
+libc_hidden_def (__netlink_assert_response)

sysdeps/unix/sysv/linux/netlinkaccess.h

@@ -19,6 +19,7 @@
 #define _NETLINKACCESS_H 1
 
 #include <stdint.h>
+#include <sys/types.h>
 #include <asm/types.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
@@ -48,5 +49,10 @@ extern void __netlink_close (struct netlink_handle *h);
 extern void __netlink_free_handle (struct netlink_handle *h);
 extern int __netlink_request (struct netlink_handle *h, int type);
 
+/* Terminate the process if RESULT is an invalid recvmsg result for
+   the netlink socket FD.  */
+void __netlink_assert_response (int fd, ssize_t result)
+  internal_function;
+libc_hidden_proto (__netlink_assert_response)
 
 #endif /* netlinkaccess.h */